


full moon

by virophilia



Category: BanG Dream! Girl's Band Party! (Video Game)
Genre: Alternate Universe - Werewolf, F/F, Smut, Trans Character, not proofread we die like men, this is literally just self indulgent bullshit
Language: English
Status: Completed
Published: 2021-01-06
Updated: 2021-01-06
Packaged: 2021-03-16 22:20:43
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,622
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/28589433
Author URL: https://archiveofourown.org/users/virophilia/pseuds/virophilia
Summary: “You know, I never thought I would own a dog. I’m more of a cat person.”“Of course, you already knew that.”
Relationships: Hikawa Sayo/Minato Yukina
Comments: 5
Kudos: 47





	full moon

**Author's Note:**

> first fic i complete in literal months and it’s smut ahaha

“You know, I never thought I would own a dog. I’m more of a cat person.”

All she received in response was a growl. She chuckled, tugging at the chain in her hand. “Of course, you already knew that.” Her other hand reached out, fingers running through fur. So soft, so nicely kept, yet rough to the touch. Not that she disliked it. Quite the opposite, actually. There was another growl.

“Be patient . . .” The moonlight passed through the sliding door, reflecting off the cyan colour. “Sayo. The night has just begun.”

* * *

It started when Sayo suddenly started excusing herself from practice once a month. It was completely out of character for her to do so unless told to by another band mate. When asked about it, she would give an excuse like “Hina insisted I help her with something,” or “I promised to make dinner tonight.” It didn’t affect her playing, so it didn’t seem like something that needed to be questioned.

But Yukina could not help worrying about the guitarist. Sayo always seemed a bit worried when she left on those days, hurrying and only stopping if someone called for attention. Was something going on that she had not told the others? Doubting Sayo made Yukina feel a bit guilty, though she tried to brush it off by telling herself she was only worried.

“Sayo,” she called, “are you heading home already?”

“Yes. I apologise, Minato-san. I’ll make sure I practice at home.”

For a moment, something flashed across her face, an emotion that Yukina couldn’t decipher. She frowned in return. Standing from the amp she had made her seat during their break, she grabbed her own school bag. “M-Minato-san?” Sayo questioned, faltering for a moment.

“Let’s end here for today. I’ll walk with you, Sayo.”

“Ah, there’s no need . . .”

“It’s not a problem. Unless you don’t desire my company?” An underhanded move, one Yukina wouldn’t use under normal circumstances. She knew this, and pushed down any negative thoughts that might come from it. Concern. It was just concern. That’s what she told herself.

“Going on a date without me? How cruel, Yukina!” Lisa came up behind them, giving Yukina a light slap on the shoulder. At the remark, Sayo’s cheeks flared red, and she looked away. Yukina said nothing, only shrugging at the joke. “You’re free to join us, if you want.”

“Ah, no, it’s fine, it’s fine! I wanted to drop by the convenience store and visit Moca, anyway. See you guys tomorrow!” And with that, the cheerful gyaru was gone.  _ One to talk about going on a date,  _ Yukina thought, suspecting there was a little more between Lisa and their rival band’s guitarist. As long as it didn’t affect their performance, Yukina didn’t mind.

Rinko and Ako were going to head out together, as they usually did, leaving Yukina and Sayo alone together. It wasn’t as if things were awkward between them; no, they understood each other far too well for it to end up like that. Though, Sayo seemed to be spacing out as they walked. Most definitely out of character.

To break the silence, Yukina spoke up, “Sayo? Is something the matter?”

“. . . No, nothing.” And after that, it went back to silence. But unlike before, where it would be comfortable and fitting, the air was tense. Something clearly was wrong, and Sayo wasn’t admitting to it. Yukina bit her lip, trying to find the right words. Maybe she should have insisted Lisa tagged along. She was the talkative one in situations like this.

Soon enough, they arrived at Sayo’s house. The sun was still setting, an orange hue tinting the sky. Sayo seemed to rush to her front door, barely turning as she said “Goodbye, Minato-san.” The door was already closed by the time Yukina opened her mouth, and she stood in silence, dumbfounded. 

She should leave. There was no point in harassing Sayo. When the time was right, she would say something. But as Yukina turned to leave, her stomach churned, and she felt as though it would be wrong to simply walk away. She didn’t know what she was doing. When she raised her hand to knock, she knew it was too late to turn back.

The one who answered the door was Hina. “Yukina-chan!” She exclaimed, eyes sparkling. “What brings you here?”

“Ah, Sayo . . . Is Sayo home?” Of course she was. Yukina literally just watched her walk in. Why was her mind suddenly blank? Hina blinked. Once. Twice. Three times. Definitely not what Yukina was expecting, but she was even more surprised when Hina turned her head to face the stairs before finally answering, “Just a sec!” The younger twin rushed up the stairs, leaving the door open, so Yukina invited herself in.

As she sat on the couch, her hands clasped together, the pit in her stomach grew larger. Was Sayo okay? The way Hina was acting only made her anxiety about the situation worse. Perhaps it was a family matter, something she had no right to intrude on. It might be best to leave.

It was when some shouting was heard that Yukina stood, making her way to Sayo’s room without a second thought. She knew that Sayo and Hina’s relationship was a strained one, but they had seemed to resolve their issues to a point where Sayo was much calmer when dealing with her sister. This was not the voice of the Sayo she knew. Usually so calm, firm, but caring and with resolve.

Hina was blocking the doorway, face tense, and when Yukina approached, she was unable to stand in the way. “Sayo!” Yukina spoke, but what was meant to be a shout of concern came out more like a whisper. Before her was undoubtedly Sayo. Sayo, the guitarist of Roselia, and one of Yukina’s closest confidants. And sprouted from her head was a pair of ears - pointed ears of a canine. 

“Out!” She screamed, shielding herself as if it would make her disappear completely. “Get out! Now!” The harsh tone made Yukina flinch back, and Hina gently took her arm, leading her away from the door as it clicked into place. For a moment, they stood there, Yukina staring at the door and Hina at the floor. Then, the younger one perked up, saying, “How about a cup of coffee?”

Back downstairs, Yukina sat on the couch again while Hina prepared some coffee in the kitchen. When she emerged, she held two mugs, and took a seat next to Yukina. “I guess she hasn’t told you,” she said, blowing gently over her mug. Yukina shook her head, barely able to hold her own. She was shaking, only a bit, but enough to make the world feel as though it was no longer tilted on its axis.

“She would probably prefer to tell you herself, but she won’t in the state to do so until the night is over.” Hina took Yukina’s mug, placing it on the coffee table, and a quiet “thank you” was mumbled. “Onee-chan is a werewolf.” The statement was as calm as Hina could ever possibly be, and she looked as if she were staring into another dimension completely. 

“It started a few months ago. She came home from practice one night, a bite mark on her arm. She looked as calm as always, but I could tell she was afraid. She told me she saw something in the dark, and from the shadow on the streetlight, she assumed it was just a dog. It attacked her when she approached, and after I patched her up, she went to bed without a word.”

This came as a shock to Yukina. Not once had Sayo implied she had been injured, attending practice as if nothing were wrong. She chastised herself for not paying closer attention. Hina continued, “The next month, when she came home from practice, she was sweating. I helped her to her room, and after a few hours, when she didn’t come down for dinner, I went to check on her. I know I shouldn’t enter her room without asking first, but I was worried. And that’s when I saw her.

“She was still my Onee-chan. I knew that much. But she was more like a beast. Not just in appearance. She didn’t attack me, but she looked as if she was prepared to. Before she could let herself, she escaped out the window. I don’t know what she’s out there doing on the nights of the full moon, but I let her know I’m always here for her.”

The story ended there. Yukina just stared at Hina, trying to wrap her head around it all. Sayo was a werewolf. Every day she had gone home early . . . they lined up with the nights there was a full moon. If she hadn’t seen it for herself, Yukina would think Hina was pulling a prank. Her gaze drifted to the staircase again, wondering if it was painful.

“And what about you?” The words snapped her from her trance, and she turned to Hina, tilting her head. “What do you mean?”

“Will you be there for Onee-chan, no matter what?”

Yukina had to take a moment to think. Normally, she would side with Sayo without asking questions. But knowing Sayo had been attacked by another werewolf, did that mean she was also attacking people? She needed to know before she could answer. Standing, she excused herself, heading out without looking back. She didn’t need to. She knew that Hina was staring holes into her back.

* * *

Sayo wasn’t at practice. It made sense. That didn’t mean it was any easier for Yukina to focus. “Hey, why don’t we stop? I think we’ve practiced long enough.” As usual, Lisa was the voice of reason, sensing Yukina’s unease. She would’ve suggested they not practice at all before they started, only hesitating because she knew how determined Yukina was.

As much as Yukina didn’t want to admit it, she knew Lisa was right. She was in no shape to continue like this. Every time she tried to clear her mind, all she could think about was Sayo shouting at her, the ears on her head, Hina’s story. It wasn’t fear that made her hesitate the night before. It was the seeds of doubt that had already been planted.

“Want me to walk home with you?” Lisa, oh Lisa. Always kind and caring, unafraid to show her concern openly. How Yukina wished she could have that trait. She shook her head, “I have somewhere else to go today. You go ahead and head home.” Even though her eyes said she wanted to resist, Lisa nodded, leaving after Rinko and Ako.

It would probably come as no surprise to anyone that Yukina was visiting Sayo. Rinko had stated that she was in class, but seemed to be dozing off the entire day. She didn’t even give notice for missing practice, but this time, Yukina would allow it. She owes that much to Sayo, after all. 

Before she could even knock, the door opened. Unlike the night before, it was Sayo who opened it. “I’ve been expecting you,” she said, making room for Yukina to enter. Without a word, she did so. Despite coming in with explicit permission like she did the other night, Yukina didn’t dare take a seat. Instead, she followed Sayo up to her bedroom.

Sayo took a seat in her desk chair and gestured for Yukina to sit on her bed, but she didn’t. She stood, staring down at Sayo. She had to say something, and she knew it. Her mouth was so dry. She licked her lips, trying to find the words. Nothing came.

“. . . Are you afraid of me?” As Sayo spoke, she trembled. The sight made Yukina want to scream. “I understand if you are. Hina told you the story, didn’t she? I don’t think I have to validate it, considering what you saw last night. Minato-san, I understand if you’re afraid, but—”

“What do you do on the nights of the full moon?”

“Huh?”

“I said, what do you do on the nights of the full moon? Hina said you go out.”

“So she told you that much . . .” There was a sad look upon Sayo’s face. Were Yukina’s suspicions true? Was Sayo attacking innocent people? Sayo being a werewolf was one thing, but if she— 

“I go out to the forest, near the shrine. I didn’t want to be like the one that attacked me on that night. So I stay in the forest. And it’s not like I look like a big dog . . . It’s much more gruesome. If someone were to see me in the city, I can only imagine what sort of stories might spread.

“I usually hunt animals. When I’ve transformed, I gain this sort of instinct . . . a sort of bloodlust. So I hunt whatever I find. And when I wake up, I’m usually back home. I guess Hina goes out to look for me and brings me home so I can get ready for school . . .”

Lisa had mentioned Hina seeming tired a few times over the last few months. It wasn’t that much of a surprise that she took care of Sayo in that state. Yukina needed another moment to process. She finally sat, crossing one leg over the other and placing a hand upon her chin. Sayo grew quiet. She was probably worried over what Yukina was thinking.

Sayo didn’t hurt people. Her playing had not faltered. Was there anything else to say? Yukina opened her mouth, only to close it again, lips pursed. Something else was on her mind. A crazy suggestion, but a suggestion nonetheless. It just depended on whether Sayo would agree to it or not.

“Sayo.” When her name was called, her head shot up, eyes hopeful.  _ Cute.  _ “I have one condition if you wish to stay in Roselia.”

“Wh-What is it?! I’ll do anything!”

Yukina sucked in a breath.  _ Here goes nothing.  _ “On the nights of your transformation, you must come over to my place.”

“Eh?”

“As the one and only guitarist of Roselia, you must be in peak condition at all times. I wish to keep an eye on you. I’ll feed you, so there are no worries there.” The thought of watching Sayo ravage an innocent animal made Yukina’s stomach heavy, but she would do it. But at the suggestion, Sayo blushed. Was it that embarrassing? It might not be the best idea.

“Minato-san, there’s one other thing I neglected to mention.”

“What’s that?”

“The bloodlust only comes after . . . normal lust.”

That was definitely unexpected. With wide eyes, Yukina had to consider this new piece of information. Would she be able to handle being in the same room with a lustful creature, one far from a regular human? But perhaps it was a perfect opportunity. Clearing her throat, she nodded. Then she smiled.

“Very well.”

* * *

The next month had been spent preparing for having Sayo over. Her parents were most definitely giving her strange looks when she came home with a bundle of chains, but dismissed it soon enough. At the pet store, she asked for the biggest collar available, but wasn’t sure if it would fit Sayo. She still hadn’t seen Sayo’s complete transformation.

She was sure that Sayo was nervous about their arrangement. When she agreed to it, she was certainly hesitant, but still did, stating she trusted Yukina. The thought made her smile. Now it was just waiting for school to finish. Practice had already been called off, and the others didn’t say much of it. It seemed Rinko and Ako had some NFO event to grind for, and Lisa was already taking the day off because of work.

The final bell chimed after what felt like the longest day of her life, and Yukina stood, quickly making her way to the exit. Was the feeling in her chest excitement or anxiety? She couldn’t decipher it. Emotions were hard. But at the entrance, Hina interrupted her escape.

“Hey there, Yukina-chan!” She called, and suddenly, Yukina’s feet slowed. She didn’t notice how fast she had been walking. “Hina,” she acknowledged, coming to a stop. The younger Hikawa was smiling brightly. She surely knew of Sayo and Yukina’s arrangement, since she was the one tending to Sayo before. They walked together, heading for the gates.

“So,” she started, “you must’ve made up your mind.”

“Yes. Sayo is precious to me.”

“More precious than you’re willing to admit, I bet.”

Before Yukina could question Hina’s words, she was gone. That’s how she was. But the words were now trapped within Yukina’s mind.  _ More precious than you’re willing to admit, I bet.  _ What could that possibly mean? Could it be that Hina knew what Yukina was struggling with to understand about herself? It was a possibility. She was perceptive, despite her appearance.

Sayo was waiting at the gate, leaning against the wall with her arms crossed. In the sunlight, she looked magnificent. Yukina had to admire it for a moment, but only a moment, no longer. She soon approached, and Sayo looked down at her, a nervous smile tugging at her lips.

“Shall we go, Minato-san?”

* * *

Her parents questioned why Sayo wasn’t joining them for dinner, but Yukina simply brushed it off by telling them she wasn’t feeling too well and needed to rest. It wasn’t as if she could tell them their guest was transforming into a beast upstairs.  _ Beast.  _ The thought left a disgusting taste in Yukina’s mouth, and her appetite was gone. Thanking her mother for the meal, she headed to her bedroom.

Upon entering, Sayo was already transforming. When they arrived, after the formal greeting to her parents, they prepared. Yukina suggested the collar, but Sayo said it was still too small. So instead, they carefully wrapped her arms and neck in chains.  _ “Tightly,”  _ Sayo had demanded.  _ “If they’re too loose, they might come undone.” _

The ears had already come out, as well as a tail, wagging wildly. Her hands were slowly becoming claws, nails sharp. Her mouth had not yet shifted to a snout, but Sayo explained beforehand that the process was slow, and would not be complete until the moon was out. It was late evening, the sun already having set, but the moon was still a bit shy in the sky.

“Please don’t look, Minato-san,” were Sayo’s words when Yukina entered. So she did not. As much as she wanted to wipe away Sayo’s sweat, make sure she was comfortable and secure, she did not. Instead, she closed the curtains to her sliding door and lied on the bed, facing the opposite direction of Sayo. 

Every minute felt like an hour. When an hour passed, it felt like an eternity. There were the sounds of bones cracking into different places, as well as Sayo’s groans. No doubt Sayo was in pain. Every bit of Yukina wanted to comfort her through the process, hold her tight and try to reassure her it would be alright. But she made a silent promise not to look.

It was only when the groans were replaced with heavy panting and growls that Yukina looked. On the floor sat Sayo, fully transformed. It was like a werewolf out of a fantasy world, standing on her hind legs, muscular arms tied together in front of her. The chain that was wrapped around her neck had also been secured around the desk, but now Yukina had no doubts that Sayo could rip it from the floor without a second thought.

Her fur was cyan, reminding Yukina that this was not just a beast in her room. It was Sayo Hikawa, guitarist of Roselia. She was eyeing Yukina down, and if she had control of her arms, she might’ve pounced. Hesitantly, Yukina stood from her bed, approaching. Even if Sayo was taller than her to begin with, their height difference was now something else entirely. Sayo must’ve been at least six feet tall now.

She reached up, placing her hand against Sayo’s snout. Despite her looks, she leaned into the touch, and Yukina felt her heart flutter.  _ Cute, cute, cute.  _ It was time. First, Yukina unwrapped the chain from the desk, keeping a firm hold of it in case she needed to tug Sayo into place. Next, she undid the chains around Sayo’s wrists, letting them fall to the floor with a thump. Her parents were heavy sleepers and the walls weren’t exactly thin, so she wasn’t worried about waking them.

Gently, she led Sayo to the bed, lying down. Sayo’s hands were at the sides of her head, and ever so gently, Yukina whispered, “Come here.” Doing as told, Sayo leaned in, attempting to kiss her. It wasn’t really a kiss, more of Sayo licking Yukina’s face as she opened her mouth, but it was a start. They continued like that for a few minutes until Yukina couldn’t take more slobber and a large tongue. 

When Yukina gave her a slight shove to the head, Sayo already began to move, as if knowing what to do. Yukina wondered if she had done this before. She tried not to think too hard about it. It was then that she realised she made the mistake of not stripping beforehand, as Sayo didn’t hesitate to rip her shirt off and snap her bra in half with the flick of a claw.

Feeling exposed was out of the question now, and Yukina slightly raised her chest. Sayo was staring, and it was only then that Yukina realised her eyes had turned gold. While they were a beautiful shade, she much preferred the usual emerald. Sayo’s tongue darted out of her mouth and she licked the entirety of Yukina’s left breast. 

A moan came from Yukina, and she covered her mouth, her shame finally getting to her. The act didn’t make Sayo stop — quite the opposite, actually. She eagerly lapped at the breast, soon switching to the other. Yukina’s skin tingled, feeling as if she had been set ablaze. She never realised how sensitive her breasts were. Sure, she had toyed around by herself a few times, but it was nothing like this.

It seemed Sayo’s patience was thin, though. She was already moving again, Yukina’s pants and panties meeting the same fate as her shirt and bra. Had it not been for the heat Sayo’s body was emanating, she was sure she’d be cold. When she felt the wet muscle against her crotch, she gasped, which was followed by another moan that managed to escape through her fingers.

Unintentionally, she tugged at the chain, still tightly clutched in her fingers and the cold metal pressing against her face. Immediately, Sayo stopped, eyes filled with concern. Even now, she was worrying about Yukina. Of course. With a weak smile, Yukina shook her head, using her free head to pet Sayo’s head. “Continue,” she managed to say, “please.”

Without waiting another second, Sayo dived back in, fiercely licking Yukina’s most indecent place. Her hips bucked into the snout, rolling with each lick, begging for more. She could no longer tell what was her own wetness and what was slobber from Sayo’s tongue. All she knew is that she wanted  _ more. _

Orgasm was nothing Yukina had managed to achieve on her own. In the past, when she tried masturbating, she only felt herself grow frustrated and give up, claiming it was taking away time from practice. But now, she was seeing stars, vision going white as a feeling she couldn’t describe overtook her. She might’ve screamed, if not for the fear she might wake her parents. The walls weren’t  _ that  _ thick.

When she finally started to come down, she frantically patted Sayo’s head, pleading for her to stop. Sayo did as told, slowly moving away. There was a wet spot under her legs, and Yukina made a silent note to wash her sheets in the morning. Though, when Sayo loomed over her, it made it obvious that she wasn’t done.

From her own crotch stood a firm erection, already pressed against Yukina’s lips. At times, she nearly forgot that fact about Sayo. She passed so well. But she wasn’t sure she could take it. It was  _ long. _ Before Sayo could suddenly enter, she tugged the chain, pulling Sayo down to her face. “Slowly,” she commanded.

The tip began to wriggle in, and Yukina clutched the chain tightly, holding her breath. Even the smallest bit was enough to cause pain. But Sayo did as told, keeping her pace slow. It felt agonisingly long, but soon enough, she was in all the way. Yukina had never felt so full in her entire life. At the base, she felt a knot, and began to worry about what might happen when Sayo finished.

Was birth even possible in this form? Sayo was human first, but that didn’t mean there wasn’t a possibility. Would telling her not to cum inside make a difference? Even with her sanity still intact, she said it was instinct. Yukina made this choice. She had to face the consequences.

For a few minutes, they sat still, Sayo giving Yukina the proper time to adjust to the full length. It was so warm, and Sayo’s fur was so soft. She wrapped her arms around Sayo’s back, the width too far for her hands to meet. As the pain subsided, she knew she was safe. Sayo wouldn’t hurt her. Finally, she whispered, “Move.”

To say the bed creaked would be an understatement. Starting slow didn’t stop the bed from rocking, and Yukina could only hope her parents were sleeping through it. As the pace picked up, Sayo kept herself reeled in, making sure not to go too hard. Yukina went in for another kiss, her inner walls pulsing as the dick inside ground into her deepest parts. 

It wasn’t long before another orgasm washed over her, but Sayo kept pounding, the sensitivity wracking up a third orgasm. She was feeling tired at this point, and wondered how long it would be until Sayo finished. Her question was answered when Sayo pulled out, the tip of her cock spurting out cum all over her stomach. It was like a fountain, covering her torso completely before finally stopping.

Her free hand came to her stomach, hovering above the substance. Yukina couldn’t even begin to imagine how that would feel inside her. But she was happy that Sayo pulled out, not wanting to fret over the possibilities of pregnancy at this age. It was then that Sayo snuggled up to her, comfortably placing her head on Yukina’s stomach.

She wasn’t the only one exhausted. Her head turned to see what time it was. One in the morning already. She was not looking forward to school the next day. Instead of worrying, she gave into her exhaustion, falling asleep with the chain in one hand and the other atop Sayo’s head.

* * *

When she awoke, the sun was shining through the curtains, and she groaned. Sayo was no longer at her side, and her stomach had been wiped clean. She sat up, looking around frantically, but managed to spot a note on her nightstand. Ignoring the fact that the clock said it was past noon, she picked up the note. 

_ I told your parents that you weren’t feeling well and left for school. I hope you understand.   
_ _ —Sayo _

A sigh of relief left Yukina, and she lied back down. She read the note again, just to make sure it was Sayo’s writing. Not that there was a doubt, she just liked the way it looked. She then noticed smaller writing at the bottom.

_ I love you. _

She felt herself smile. Yukina would make sure to return the favour at practice today.

**Author's Note:**

> you can follow me on [twitter](https://twitter.com/kdhraiai?s=21) but only if you want to 👉👈


End file.
